1. Field of the Invention
The present invention relates to an on-screen display apparatus. More specifically, the present invention relates to an on-screen display apparatus for displaying characters representative of a channel number, a timer reservation time, and etc. on a display screen of a monitor television in a video display apparatus such as a television receiver, a video tape recorder, a video disc player, and etc.
2. Description of the Related Art
In such a kind of on-screen display apparatus, font data of necessary characters are stored in advance in a character memory (ROM), and the font data is sequentially read-out in accordance with designation by an user or a microcomputer. The font data are then converted into a video signal which is then superposed on a television video signal. In a conventional wellknown on-screen display apparatus, addresses of a character memory are one-by-one designated by the microcomputer each character such that the font data is read-out from the character memory each character one-by-one.
In a conventional on-screen display apparatus, in a case where a given sentence or character train is to be displayed, on-screen character data of a series of characters which constitute the sentence or character train are written in advance in a ROM of a microcomputer, and the character data is read-out and applied to the character memory each character one-by-one, and therefore, not only a memory capacity of the microcomputer increases but also a burden of the microcomputer for reading-out the character data in a sequential manner is large. Furthermore, the character data are outputted one by one character, and then, an on-screen display is performed at a stage where the character data of all characters for a whole television screen, 12 lines.times.24 characters, for example, have been written in the display memory. Thus, a speed for the on-screen display is slow and is not synchronized with a key operation by the user. Accordingly, there was a problem in the operability of the apparatus.